1. Field of the Invention
The present invention relates to an ink jet recording apparatus and its recording method for recording an image with a recording head having a plurality of orifices.
2. Description of Prior Art
A multi-droplet method is a recording method in which a plurality of ink droplets ejected from a single orifice is projected substantially onto an identical position on the recording sheet to form a pixel, and the number of ejected ink droplets of the pixel is changed to express halftoning (gray-scale) of an recorded image. The multi-droplet method is an effective for expressing a halftoning, particularly in a recording system in which ink droplets are ejected by a bubble generated in an ink fluid by thermal energy, and in which it is difficult to change the size of each ink droplet to a large extent.
As a single pixel is formed by a plurality of ink droplets ejected from a single orifice in the multi-droplet recording method, in case that the amount of ejected ink droplets varies from orifice to orifice, a density level (gray level) in the recorded image cannot maintain to be uniform and the recorded image may contain strip-noises or shadings (or bandings).
In order to prevent those problems, in prior art recording head, the manufacturing process of the recording heads must be controlled precisely by a software-based system for reducing the variation of the amount of ejected ink droplets from orifice to orifice. As a result, there are many problems including that a manufacturing cost may increase.
To solve the problems described above, an assignee of the present invention proposed a recording method in which a single pixel is formed by a plurality of ink droplets ejected from a plurality of orifices. That is, in the proposed method, so-called a multi-scan recording method, each of ejections of ink droplets for forming a single pixel from each of a plurality of orifices is performed at respective scanning of a recording head. The method will be appreciated that the amount variation of ejected ink droplets can be distributed uniformly from orifice to orifice.
FIG. 1 is a schematic illustration illustrating the multi-scan recording method.
In FIG. 1, reference numeral 801 denotes a recording head having a plurality of orifices, in this case, the number of orifices is 128. The recording head 801 forms a recorded image by ejecting ink droplets during scanning thereof in the horizontal direction in the figure from left to right. 801A is a position of the first scanning of the recording head 801 in relative to a recording medium, and 801B, 801C and 801D are positions corresponding to the subsequent scannings of the recording head, respectively. Reference numeral 802 denotes a pixel. The number having a symbol # as its prefix is an identification number specific to each of 128 orifices. In the above structure, a density level of the specified pixel 802 at a pixel position (x, y) is expressed by selecting ejections and non-ejections from orifices No. 100, No. 68, No. 36 and No. 4 at each of four scannings 801A, 801B, 801C and 801D of the recording head 801. This means that, for example, if all the orifices do not eject ink droplets, the density level of the specified pixel 802 at (x, y) is minimized, and if all the orifices eject ink droplets, the density level is maximized. The intermediate density level between its minimum and maximum is expressed by a combination of selective ejections and non-ejections of ink droplets from orifices. In this prior art recording methods, what is explained is a recording method in which a pixel having 5 levels of the density level is formed and the number of ink ejections between 0 and 4 to each pixel is obtained by pseudo-halftoning processing such as an error diffusion method and a dither method and is stored in a memory, and in which data of the number in the memory is read out at every time of scannings, and thus, a pixel is formed by driving the recording head in responsive to this read-out data.
The ejection timing for forming the pixel 802 by each of orifices No. 100, No. 68, No. 36 and No. 4 in the scannings 801A, 801B, 801C and 801D of the recording head 801 is established by pulses from an encoder measuring the relative distance between the recording head 801 and the recording medium. After each of scannings 801A, 801B, 801C and 801D, the recording medium is transported with respect to the recording head in the direction vertical to the scanning direction by 32 times of the distance between adjacent orifices, that is, 32 pitches obtained by 128 divided by 4. By scanning four times the recording head, an image corresponding to 128 orifices can be recorded.
In the case of forming a single pixel with a single ink droplet, by selecting appropriate one of a plurality of orifices, the amount variation of ejected ink fluids from orifice to orifice can be reduced.
FIG. 2 is a schematic illustration showing an arbitrary part of an array of pixels arranged in the scanning direction of the recording head. Each pixel in the array is formed by ink droplets ejected from orifices No. 100, No. 68, No. 36 and No. 4 in the respective scanning 801A, 801B, 801C and 801D as shown in FIG. 1.
In FIG. 2, reference numerals 901 to 909 denote pixels, each number written in the pixels 901 to 909 represents the number of ejections to each pixel. The identification number of the orifice used for forming the pixel and the scanning number at which the orifice ejects an ink droplet are written below each of the corresponding pixels. For example, the number of ejections to the pixel 904 is one and the orifice No. 100 ejects an ink droplet in the scanning 801A for forming the pixel 904. And also, the number of ejections to the pixel 905 is two, and the orifices No. 100 and No. 68 eject ink droplets in the scannings 801A and 801B, respectively, for forming the pixel 905.
In FIG. 2, in the case that the number of ejections is one as to the pixels 901, 902 and 904, an ink droplet is always ejected from the orifice No. 100 in the scanning 801A. In the case that the number of ejections is two as to the pixels 905, 906 and 909, one ink droplet is always ejected from the orifice No. 100 in the scanning 801A and another ink droplet is always ejected from the orifice No. 68 in the scanning 801B. Similarly, in the case that the number of ejections is three as to the pixel 908, the orifice No. 100 is used in the scanning 801A, the orifice No. 68 is used in the scanning 801B and the orifice No. 36 is used in the scanning 801C, respectively. In the case that the number of ejections is four, all the orifices are always used in their corresponding scanning for forming a pixel.
However, in the case of forming a pixel in the above manner, if there occur, for example, in the orifice No. 100 always used, ejection failures such as disabled ejections, the less amount of ejected ink droplet, and further, ejection of ink droplet in unexpected directions, the recorded images may contain strip-noises or shadings. So far, even if a single pixel is formed by a plurality of ink droplets ejected from a plurality of orifices, there may be a case that high-quality recorded images cannot obtained and recording images is spent on too long time. In addition, a specific orifice, for example, the orifice No. 100, is used too often and other orifices are not used so frequently, and hence, there may be such problems that every orifice is not used uniformly and the lifetime of the recording head may be shorten.
This problem arises similarly in case of forming a single pixel with a single ink droplet.
An object of the present invention is to provide an ink jet recording apparatus and a recording method in which a plurality of good-conditioned orifices are uniformly used for recording images even in case that some of a plurality of orifices suffer from ejection failures and whereby the lifetime of the recording head can be enlarged.
Another object of the present invention is to provide an ink jet recording apparatus and a recording method in which the orifice used at first for each of pixels is different from one another with respect to pixels, and a plurality of orifices can be used uniformly in developing a plurality of pixels as the orifices are assigned to pixels in a designated order.
In the first aspect of the present invention, there is provided an ink jet recording apparatus for recording an image with a set of pixels formed by ejecting an ink droplet onto a recording medium, comprising:
a recording head having a plurality of discharging portions from each of which the ink droplet is ejected;
a driving means for making the recording head eject the ink droplet according to driving data; and
a data setting means for assigning the driving data to a plurality of individually different discharging portions so as to form each one of the pixels by means of a plurality of ink droplet ejected from a plurality of individually different discharging portions, which are different from one of the pixels to another of the pixels.
Here, the ink jet recording apparatus may further comprise a scanning means for performing a scanning operation of the recording head for recording, and each of a plurality of individually different discharging portions is used to eject an ink droplet in respective different scanning of the recording head.
The recording head may generate a bubble in an ink fluid by thermal energy and eject the ink droplet in responsive to generation of the bubble.
The data setting means may assign a plurality of driving data to a plurality of individually different discharging portions in a predetermined order, and the discharging portion assigned at first to each of the pixels is different from one of the pixels to another of the pixels.
The discharging portion assigned at first may be one next to the discharging portion assigned in the previous data setting of the pixel in the predetermined order.
The predetermined order may be an sequential order of a plurality of individually different discharging portions.
The predetermined order may be a sequential order of a plurality of individually different discharging portions, and the discharging portion assigned at first is determined in accordance with a position of a corresponding pixel in a set of pixels.
The predetermined order may be a sequential order of a plurality of individually different discharging portions, and the discharging portion assigned at first may be determined randomly.
In the second aspect of the present invention, there is provided an ink jet recording apparatus for recording an image with a set of pixels formed by ejecting an ink droplet onto a recording medium, comprising:
a plurality of recording heads each of which has a plurality of discharging portions, each of a plurality of recording heads ejecting individually different kinds of ink droplets from each of a plurality of discharging portions, respectively;
a driving means for making a plurality of recording heads eject respective ink droplets in responsive to driving data; and
a driving data setting means for assigning the driving data to a plurality of individually different discharging portions of a plurality of recording heads so as to form each one of the pixels by means of a plurality of ink droplets ejected from a plurality of individually different discharging portions of a plurality of recording heads, identical kinds of ink droplets of a plurality of ink droplets being ejected on different positions from one another in each one of the pixels, and the discharging portions to which the driving data are assigned at first in a plurality of recording heads ejecting ink droplets on identical positions with one another.
Here, an ink jet recording apparatus may further comprise a scanning means for performing a scanning operation of a plurality of recording heads for recording, and each of a plurality of discharging portions in each of a plurality of recording heads ejects a respective kind of ink droplet in respective different scanning of the recording head.
Each of a plurality of recording heads generates a bubble in an ink fluid by thermal energy and ejects the ink droplet in responsive to generation of the bubble.
In the third aspect of the present invention, there is provided an ink jet recording apparatus for recording an image with a set of pixels formed by ejecting an ink droplet onto a recording medium, comprising:
a recording head having a plurality of discharging portions from each of which the ink droplet is ejected;
a driving means for making the recording head eject the ink droplet according to driving data; and
a data setting means for assigning the driving data to one of a plurality of discharging portions so as to form each of the pixels, one of a plurality of discharging portions being different from one of the pixels to another of the pixels.
Here, the ink jet recording apparatus may further comprise a scanning means for performing a scanning operation of the recording head, and one of a plurality of discharging portions ejects the ink droplet in respective different scanning of the recording head.
The recording head may generate a bubble in an ink fluid by thermal energy and eject the ink droplet in responsive to generation of the bubble.
One of a plurality of discharging portions may be different from one of the pixels to another of the pixels in the direction of the scanning of the recording head.
One of a plurality of discharging portions may be different from one of the pixels to another of the pixels in the direction of array of a plurality of discharging portions.
The driving data may be a gray scale level data, and each of the pixels may be formed by means of one or more ink droplets ejected from a plurality of discharging portions.
In the fourth aspect of the present invention, there is provided an ink jet recording method for recording an image with a set of pixels formed by ejecting an ink droplet onto a recording medium, comprising the steps of:
providing for a recording head having a plurality of discharging portions from each of which the ink droplet is ejected;
assigning driving data to a plurality of individually different discharging portions so as to form each one of the pixels by means of a plurality of ink droplets ejected from a plurality of individually different discharging portions, which are different from one of the pixels to another of the pixels; and
making the recording head eject the ink droplet according to the driving data assigned.
Here, the ink jet recording method may further comprise a step for performing a scanning operation of the recording head for recording, and each of a plurality of individually different discharging portions is used to eject an ink droplet in respective different scanning of the recording head.
The recording head may generate a bubble in an ink fluid by thermal energy and eject the ink droplet in responsive to generation of the bubble.
The assigning step may assign the driving data to a plurality of individually different discharging portions in a predetermined order, and the discharging portion assigned at first to each of the pixels is different from one of the pixels to another of the pixels.
The discharging portion assigned at first may be one next to the discharging portion assigned in the previous data setting of the pixel in the predetermined order.
The predetermined order may be a sequential order of a plurality of individually different discharging portions.
The predetermined order may be a sequential order of a plurality of individually different discharging portions, and the discharging portion assigned at first may be determined in accordance with a position of a corresponding pixel in a set of pixels.
The predetermined order may be a sequential order of a plurality of individually different discharging portions, and the discharging portion assigned at first may be determined randomly.
In the fifth aspect of the present invention, there is provided an ink jet recording method for recording an image with a set of pixels formed by ejecting an ink droplet onto a recording medium, comprising the steps of:
providing for a plurality of recording heads each of which has a plurality of discharging portions, each of a plurality of recording heads ejecting individually different kinds of ink droplets from each of a plurality of discharging portions, respectively;
assigning driving data to a plurality of individually different discharging portions of a plurality of recording heads, so as to form each one of said pixels by means of a plurality of ink droplets ejected from a plurality of individually different discharging portions of a plurality of recording heads, identical kinds of ink droplets of a plurality of ink droplets being ejected on different positions from one another in each one of the pixels, and the discharging portions to which the driving data are assigned at first in a plurality of recording heads ejecting ink droplets on identical positions with one another; and
making a plurality of recording heads eject respective ink droplets in responsive to the driving data assigned.
The method may further comprise a step for performing scanning operations of a plurality of recording head for recording, and each of a plurality of discharging portions in each of a plurality of recording head ejects a respective kind of ink droplet in respective different scanning of the recording head.
Each of a plurality of recording heads may generate a bubble in an ink fluid by thermal energy and eject the ink droplet in responsive to generation of the bubble.
In the sixth aspect of the present invention, there is provided recording method for forming a pixel on a designated line on a recording medium by scanning a recording head ejecting an ink fluid from a plurality of discharging portions, comprising the steps of:
selecting a plurality of discharging portions which can be used for forming said pixel on the designated line;
determining the discharging portion used for forming the first pixel on the designated line in accordance with ejection data corresponding to an ejection from a plurality of selected discharging portions onto the first pixel; and
determining the discharging portion used for forming the second pixel on the designated line among a plurality of selected discharging portions in accordance with data corresponding to an ejection from the discharging portion determined to be used before a plurality of selected discharging portions to the second pixel.
The ejection data may be defined as gray scale level data, and the pixel on the designated line may be formed by a single ink droplet or a plurality of ink droplets ejected from a plurality of discharging portions.
The discharging portion used for forming the second pixel may be determined in a predetermined order among a plurality of selected discharging portions.
The recording head may generate a bubble in an ink fluid by thermal energy and ejects the ink droplet in responsive to generation of the bubble.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.